沙化和退化状态对甘南草地生态系统固碳的影响

Effects of desertification and degradation on carbon sequestration of grassland ecosystem in Gannan

陆地生态系统作为全球第二大碳库,其碳收支应对气候变化一直是研究的热点领域。多数研究主要探讨温/湿度、CO_(2)浓度等对陆地生态系统碳循环的影响,而针对草地的沙化、退化对植被整个固碳过程所产生影响的研究相对不足。本研究以30 m×30 m空间分辨率的遥感数据做支撑,参考国家标准GB/T 24255—2009解译草地沙化和退化数据,并结合光能利用率遥感模型,模拟陆地生态系统总初级生产力(GPP)、净初级生产力(NPP)和净生态系统生产力(NEP),分析甘南地区植被固碳的时空变化特征,最后讨论草地沙化和退化对植被固碳所产生的影响。结果表明:甘南地区的草地主要呈现无沙化和轻度沙化状态,并伴随着较少区域面积不同程度的土地退化现象,其中玛曲县的草地沙化和退化情况相对严重,草地沙化和退化面积分别占甘南地区总面积的0.03%和2.50%;研究区草地GPP、NPP和NEP均具有上半年呈递增、下半年呈递减的月变化特征,而在空间格局上呈现为东高西低、北高南低的分布特征;其中,玛曲县是草地年固碳量最大的县,其草地固碳量为691.28 t C·a^(-1),唯舟曲县为碳源,其NEP值为-88.64 t C·a^(-1);GPP、NPP和NEP随草地极重度沙化、重度沙化、中度沙化、轻度沙化和无沙化呈显著递减趋势显著,而草地退化对甘南地区GPP、NPP和NEP影响不显著。本研究为揭示陆地生态系统碳循环的动态机制提供一定的依据,为完善甘南地区碳减排政策的制定提供数据支撑。

As the second largest carbon pool of the world, terrestrial ecosystems have always been a hot research field with respect to the responses of their carbon budget to climate change. Most studies mainly focus on the effects of temperature, humidity, and CO_(2)concentration on carbon cycle of terrestrial ecosystems, but the studies on the effects of desertification and degradation of grasslands on carbon sequestration processes of vegetation are relatively insufficient. In this study, we used remote sensing data with a spatial resolution of 30 m×30 m, to decipher grassland desertification and degradation data with a reference of the national standard GB/T 24255-2009. We simulated gross primary productivity(GPP), net primary productivity(NPP) and net ecosystem productivity(NEP) with a remote sensing model of light energy utilization. We analyzed the temporal and spatial variations of vegetation carbon sequestration and the role of grassland desertification and degradation in Gannan. The grassland mainly presented a state of no desertification or light desertification, and was accompanied by small dispersed areas of land degradation with varying degrees. Among them, grassland desertification and degradation were relatively serious in Maqu County. Grassland desertification and degradation areas accounted for 0.03% and 2.50% of the total study area, respectively. The GPP, NPP, and NEP of grassland in Gannan were characterized by monthly increasing in the first half of the year and decreasing in the second half of the year. The spatial pattern was characterized by the distribution of high in the east and low in the west, high in the north and low in the south. Maqu was the county with the largest annual carbon sequestration of grassland(691.28 t C·a^(-1)). Among all the counties, only Zhouqu County was a carbon source, with a NEP of-88.64 t C·a^(-1). GPP, NPP, and NEP showed a significant decreasing trend along with extremely severe, severe, moderate, light, and no desertification, while grassland degradation did not affect GPP, NPP, and NEP in Gannan. Our results provide basis for revealing the dynamic mechanism of terrestrial ecosystem carbon cycle and data support for the formulation of carbon emission reduction policies in Gannan.